Underdrain excavation apparatus

ABSTRACT

Provided is an underdrain excavation apparatus by which, while an underdrain is excavated in the ground, a hydrophobic material and/or a water-holding material (functional material) can be filled in the underdrain executed in a smooth and reliable manner. In the underdrain excavation apparatus, a soil cutting shank  11  which is vertically held and a bullet-like underdrain borer  12  which is provided on a lower end of the soil cutting shank  11  are pulled in a horizontal direction by a bulldozer  14  to excavate an underdrain  22  in a ground  21,  and a functional material supplied via a functional material transport line  13  provided in the soil cutting shank  11  and in the underdrain borer  12  is filled in the underdrain. A gas flow generator generating a gas flow by jetting a high-pressure gas supplied from a high-pressure gas generator into a tubular body is connected with the functional material transport line  13.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an apparatus for excavating an underdrain for draining water from the ground of a highly damp area such as a rice paddy and/or for retaining water in a dry land.

[0003] 2. Description of the Prior Art

[0004] In order to improve drainage of a highly damp area such as a rice paddy, an underdrain has been excavated in the ground using an underdrain excavation apparatus. An underdrain excavation apparatus has a vertically held soil cutting shank and an underdrain borer having a bullet form provided on a lower end of the soil cutting shank. When used, the apparatus is attached to a rear part of a work vehicle such as a bulldozer or tractor. The work vehicle is advanced in the state where the underdrain borer is arranged at a low position and the lower half of the soil cutting shank is inserted in the ground so that the soil cutting shank is pulled in a horizontal direction to excavate an underdrain in the ground.

[0005] In an underdrain excavated by the advance of a bullet-like underdrain borer, a perforated pipe for supplying/draining water is sometimes laid. For laying the pipe, some methods have been proposed: a method in which the distal end of a perforated pipe is coupled with the rear part of an underdrain borer and the perforated pipe is drawn from a perforated pipe supplying device arranged at the starting point of the excavation into an underdrain by the advance of an underdrain excavation apparatus to lay the perforated pipe; a method in which a plastic sheet is embedded in an underdrain while the sheet is being formed circularly by a molding machine; a method in which a hydrophobic material such as rice husks is filled while an underdrain is being excavated; a method in which a pipe is laid and a hydrophobic material is filled while an underdrain is being bored, and the like.

[0006] There is an underdrain excavation apparatus disclosed in Unexamined Japanese Patent Application No. Sho 56-156310 as an apparatus employed in underdrain construction as described above. By employing this type of underdrain excavation apparatus, it is possible that a pipe for supplying/draining water is laid while an underdrain is being excavated in the earth and, simultaneously, a hydrophobic material is filled in the space between the underdrain and the pipe.

[0007] In a conventional underdrain excavation apparatus, rice husks filled in an underdrain as a hydrophobic material are stored in a hopper so as to be fed out continuously from the hopper by a feeding device with the progress of underdrain excavation and to be merely dropped into an underdrain via a predetermined transport line. Thus, rice husks are not always supplied to the underdrain continuously, and are likely to clog the transport line or to be interrupted. Therefore, rice husks are sometimes not completely filled in an underdrain, thereby causing uneven filling, voids or the like.

[0008] When rice husks are not completely filled in an underdrain, the function of the underdrain deteriorates, and thus drainage effect cannot be obtained as expected.

[0009] By the way, desertification of green tracts of land has progressed on a global scale and has been pointed out and is well known as a serious problem. If plants can take root even in such dry land, it would revive previously green tracts of land and be an effective countermeasure even for a variety of political disputes sometimes arising during a food crisis or when people abandon dried-up land to migrate. For this reason, aggressive research and experiments for creating or generating green tracts of land have been made. For example, as an impermeable layer, a film-like or sheet-like high molecular material is buried in the ground of a desert, thereby turning the stratum over the film into arable land. The film to be buried for this purpose should be of large dimension and high strength, and the film should durable and resistant to sunlight. Furthermore, the film must also be resistant to microbial decomposition in the ground. However, to lay films over a large area is difficult work, and thus far no equipment exists to resolve this problem.

[0010] The first object of the present invention is to provide an underdrain excavation apparatus by which an underdrain can be excavated in the ground and a hydrophobic material or a water-holding material (hereinafter, referred to as a functional material) can be filled in the underdrain in a smooth and reliable manner.

[0011] In the conventional underdrain excavation apparatus described above, the soil cutting shank is provided only in the rear part of a traveling device. As a result, in the case where an underdrain is excavated in a farmland having border ridges which are the elevated footpaths commonly built around each individual rice field, the traveling device cannot run up onto the border ridge and move. Thus, the soil cutting shank is detached from the traveling device before a border ridge, and the traveling device does a U-turn so that the soil cutting shank is coupled with the rear part thereof. Then, construction is continued while the traveling device goes back.

[0012] Such a construction method has the following problems:

[0013] (1) Since it is necessary to make the traveling device do a U-turn, the whole work takes a longer time, lowering the work efficiency.

[0014] (2) A U-turn is sometimes difficult in a narrow space.

[0015] (3) After a U-turn, it is difficult to position the traveling device for coupling the soil cutting shank.

[0016] The second object of the present invention is to provide an underdrain excavation apparatus by which an underdrain in a farmland can be constructed without doing a U-turn even where there are border ridges.

SUMMARY OF THE INVENTION

[0017] In order to achieve the first object, an underdrain excavation apparatus according to the present invention is an apparatus comprising a soil cutting shank which is vertically held, a bullet-like underdrain borer which is provided on a lower end of the soil cutting shank, a pulling means, the soil cutting shank and the underdrain borer being pulled in a horizontal direction by the pulling means to excavate an underdrain in the ground, a functional material transport line provided in the soil cutting shank and in the underdrain borer, a functional material supplied via the functional material transport line being filled in the underdrain, and a gas flow generator generating a gas flow by jetting a high-pressure gas supplied from a high-pressure gas generator into a tubular body, the gas flow generator being connected with the functional material transport line.

[0018] In the underdrain excavation apparatus of the above structure, when a high-pressure gas is supplied from the high-pressure gas generator to the gas flow generator, a gas flow is generated by the gas jetted into the tubular body; the gas flow flows in one direction inside the functional material transport line connected with a rear part of the gas flow generator; and a suction force is generated due to a negative pressure generated by the gas flow in the front part of the gas flow generator. Thus, utilizing this suction force, the functional material is sucked from the front part of the gas flow generator, and the functional material is transported riding on the gas flow flowing inside the functional material transport line, whereby the material can be filled in an underdrain.

[0019] An underdrain excavation apparatus according to the present invention is an apparatus comprising a soil cutting shank which is vertically held, a bullet-like underdrain borer which is provided on a lower end of the soil cutting shank, the soil cutting shank and said underdrain borer being pulled in a horizontal direction by the pulling means to excavate an underdrain in the ground while a supply/drain pipe is being laid in the underdrain, a functional material transport line provided in the soil cutting shank and in the underdrain borer, a functional material supplied via said functional material transport line being filled in the space between the underdrain and the supply/drain pipe, and a gas flow generator generating a gas flow by jetting a high-pressure gas supplied from a high-pressure gas generator into a tubular body, the gas flow generator being connected with the functional material transport line.

[0020] Since, with the above described structure, the functional material can be transported riding on the gas flow generated by the gas flow generator, the supply/drain pipe can be laid while an underdrain is being excavated in the ground, and filling of the functional material into the space between the underdrain and the supply/drain pipe can be executed in a smooth and reliable manner.

[0021] As the gas flow generator, by employing a Coanda spiral flow generator slantingly jetting the high-pressure gas supplied from the high-pressure gas generator from an inner peripheral surface of the tubular body toward the central axis of the tubular body to generate a spiral gas flow along the inner peripheral surface, a special spiral gas flow called the Coanda spiral flow can be generated inside the functional material transport line. Here, the Coanda spiral flow is a spiral gas flow generated along the inner peripheral surface of the tubular body or the like, utilizing the Coanda effect known as a phenomenon that a jet stream of a gas or liquid tends to flow adjacent to a direction along the curved surface of the wall even when the direction of the jet stream axis and the direction of the curved wall are distinct from each other.

[0022] By generating the Coanda spiral flow, since suction force is generated in the front part thereof, the functional material can be sucked utilizing the suction force, and the functional material can be transported to an underdrain that is the destination while the functional material is being carried on the Coanda spiral flow flowing inside the functional material transport line. In this case, since the Coanda spiral flow has a special characteristic of being slightly apart from the inner peripheral surface of the functional material transport line and of flowing while circling along the inner peripheral surface, the contact between the functional material transported by the Coanda spiral flow and the inner peripheral surface of the transport line is eliminated, whereby the functional material can be smoothly transported.

[0023] Here, by providing soil pressing members protruding in a manner like a horizontal-stabilizer on both side faces of the soil cutting shank, the ground torn by the advance of the soil cutting shank can be restored to the original state. Thus, collapse of the underdrain bored by the underdrain borer can be prevented, and the functional material is not scattered.

[0024] The soil pressing members preferably have elevation angles of about 10 to 20 degrees toward the advancing direction, have fins hanging down from the side ends thereof, and are arranged to form a V-shape opening toward the front end when looked in a plan view by the left and right parts thereof. With such shape and arrangement, the function to restore the ground torn by the soil cutting shank can be enhanced.

[0025] Furthermore, in order to achieve the second object, an underdrain excavation apparatus according to the present invention is an apparatus comprising a soil cutting shank which is attachably/detachably fixed on a fixing device provided on a traveling device, and a bullet-like underdrain borer provided on a lower end of the soil cutting shank, the soil cutting shank being pulled in a horizontal direction by the traveling device to excavate an underdrain in the ground, the fixing device being disposed on a front part and on a rear part of the traveling device.

[0026] In the underdrain excavation apparatus of the above structure, by providing the fixing device for the soil cutting shank on the front part and on the rear part of the traveling device, construction is executed in a manner that the soil cutting shank is fixed on the rear part of the traveling device until reaching a border ridge, and after the soil cutting shank is detached from the traveling device before a border ridge, the traveling device is backed straight. Then, the soil cutting shank is coupled with the front part of the traveling device so that the traveling device is again advanced from there, whereby excavation is completed up to the border ridge.

[0027] In this underdrain excavation apparatus, by providing a means for laying a supply/drain pipe in an underdrain simultaneously with excavating the underdrain by moving the traveling device, the supply/drain pipe which effectively drains water to the outside a farmland or supplies water from the outside farmland is simultaneously constructed.

[0028] By providing a means for filling a functional material supplied from the traveling device into the underdrain (when a supply/drain pipe is laid in the underdrain, into the space between the inner periphery of the underdrain and the outer periphery of the supply/drain pipe) via a functional material transport line provided in the soil cutting shank and in the underdrain borer, the functional material is smoothly supplied into the underdrain.

[0029] As the functional material, a hydrophobic material is employed in some cases as described above, and a water-holding material is employed in other cases. By employing a hydrophobic material such as rice husks, drainage of a highly damp area such as a rice paddy can be improved, and water gathered in an underdrain is effectively led to the outside a farm via the supply/drain pipe.

[0030] By employing a water-holding material as the functional material, water can be stored in an underdrain constructed in a desert or a dry land, and by appropriately supplying water from outside a farm through the supply/drain pipe, water can be effectively supplied to the ground around the underdrain.

[0031] The examples of water-holding materials may be processed and decomposed starch-polyacrylonitrile products, starch series such as starch-polyacrylate crosslinking substances, cellulose series such as carboxyl methyl cellulose, and polyacrylate series such as polyacrylic soda crosslinking substance. Water-absorbing polymer is a high polymer electrolyte, in which water molecules are bound in the inter-molecules of three dimensional network structure. While absorbing power of cotton, pulp, sponge, and the like due to capillary phenomenon is about 20 times its own weight, water absorbing polymer can absorb water of about several hundreds to thousands times its own weight.

[0032] Water absorbing polymer has a large number of hydrophilic groups in molecules, and when there is water, part of it ionizes. Then, cations are isolated in water and start pulling anions remaining in hydrophilic groups, pulling against each other. By this power, molecules of water are captured in hydrophilic groups. Water molecules are firmly held by hydrogen bonding in a fine high molecular network that spreads out in all directions. Since bonding occurs inside the network, water is not disgorged even when the material is pressurized by squeezing. Accordingly, by filling such water-holding material in an underdrain, excellent soil can be obtained without deteriorating gas permeability.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033]FIG. 1 is a side view showing an underdrain excavation apparatus in use according to the first embodiment.

[0034]FIG. 2 is a rear elevation of the underdrain excavation apparatus shown in FIG. 1 which is partly cut off.

[0035]FIG. 3A is a side view showing a soil cutting shank and an underdrain excavator constituting the underdrain excavation apparatus shown in FIG. 1; FIG. 3B is a rear elevation thereof; and FIG. 3C is a sectional view taken along the line A-A of FIG.3B.

[0036]FIG. 4 is a sectional view of the underdrain excavation apparatus shown in FIG. 1.

[0037]FIG. 5A is a sectional view showing a Coanda spiral flow generator, and FIG. 5B is a front view thereof.

[0038]FIG. 6 is a sectional view showing the Coanda spiral flow generator shown in FIG. 5 in use.

[0039]FIG. 7A is a side view showing a function of soil pressing members provided on the soil cutting shank constituting the underdrain excavation apparatus shown in FIG. 1; FIG. 7B is a rear elevation thereof, and FIG. 7C is a sectional view taken along the line B-B of A.

[0040]FIG. 8 is a side view showing an underdrain excavation apparatus in use according to the second embodiment of the present invention.

[0041]FIG. 9 is a side view showing an underdrain excavation apparatus according to the third embodiment of the present invention.

[0042]FIG. 10 is a rear elevation of the underdrain excavation apparatus shown in FIG. 9.

[0043]FIG. 11 is a sectional view of the excavated underdrain.

[0044]FIGS. 12A to 12E are enlarged views of a soil cutting shank in the present embodiment, in which FIG. 12A is a side view; FIG. 12B is a front view; FIG. 12C is a plan view; FIG. 12D is a sectional view taken on line B-B of A; and FIG. 12E is a sectional view taken along the line C-C of FIG. 12A.

[0045]FIGS. 13A to 13D are enlarged views of a clamp in the present embodiment, in which FIG. 13A is a side view; FIG. 13B is a plan view; FIG. 13C is a front view; and FIG. 13D is a sectional view taken along the line A-A of FIG.13A.

[0046]FIG. 14 is a process flow showing a construction method according to the present invention.

[0047]FIGS. 15A to 15C are views showing another construction method by a traveling device with an underdrain excavation apparatus according to the present invention, in which A is a side view showing the present construction method; B is an enlarged view of a main part; and C is an enlarged sectional view of an underdrain.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0048] [First Embodiment]

[0049]FIG. 1 is a side view showing an underdrain excavation apparatus in use according to the first embodiment; FIG. 2 is a rear elevation of the underdrain excavation apparatus shown in FIG. 1 which is partly cut off; FIG. 3A is a side view showing a soil cutting shank and an underdrain excavator constituting the underdrain excavation apparatus shown in FIG. 1; FIG. 3B is a rear elevation thereof; FIG. 3C is a sectional view taken along the line A-A of FIG. 3B; and FIG. 4 is a sectional view of the underdrain excavation apparatus shown in FIG. 1.

[0050] An underdrain excavation apparatus 10 of the present embodiment is attached to the rear part of a bulldozer 14 when used, and comprises a soil cutting shank 11 which is vertically held, a bullet-like underdrain borer 12 provided on the lower end of the soil cutting shank 11, a transport line 13 for feeding a functional material provided in the soil cutting shank 11 and in the underdrain borer 12, a high-pressure air generator 15, a hopper 17 for storing a functional material 16, a gas flow generator 18 arranged between an exhaust port 23 of the hopper 17 and the transport line 13 to be connected with each other, and an air supply pipe 19 for supplying high-pressure air from the high-pressure air generator 15 to the gas flow generator 18.

[0051] A screw conveyor 24 for feeding the functional material 16 toward the exhaust port 23 as well as a motor for rotating/driving the conveyor 24 are disposed on the bottom of the hopper 17. Horizontal-stabilizer-like soil pressing members 20 are provided on both side faces of the soil cutting shank 11, and a Coanda spiral flow generator described later is employed as the gas flow generator 18.

[0052] As shown in FIG. 1 and FIG. 2, the bulldozer 14 is advanced in the state where the underdrain borer 12 is arranged at a low position and the lower half of the soil cutting shank 11 is planted in the ground 21 so that an underdrain 22 is excavated in the ground 21, and thus the functional material 16 supplied from the inside of the hopper 17 via the gas flow generator 18 and the transport line 13 can be filled in the underdrain 22.

[0053] As shown in FIG. 5 and FIG. 6, in the gas flow generator 18, high-pressure air supplied from the air supply pipe 19 enters from a connecting port 26 into a distribution room 27. The air is decelerated and homogenized therein and flows toward a Coanda slit 28, and after passing through the Coanda slit 28, the high-pressure air is jetted slantingly and uniformly toward the central axis 29 thereof. At this time, the combination of a central axis direction vector and a radius direction vector of the jetted air generates a Coanda spiral flow 31 flowing in the central axis 29 direction along the inner peripheral surface of a tubular body 30. The Coanda spiral flow 31 has a property that the flow 31 is slightly apart from the inner peripheral surface of the tubular body 30 as well as the transport line 13 following the tubular body 30 and flows to the downstream direction while circling along the inner peripheral surfaces of the tubular body 30 and the transport line 13, and the pressure of the central part thereof becomes lower than the circumference.

[0054] Since the Coanda spiral flow 31 flows in one direction along the transport line 13 which is connected to the rear part of the gas flow generator 18 and a suction force is generated due to a negative pressure generated in the Coanda spiral flow 31 in the front part of the spiral flow generator 18, the functional material 16 fed from the exhaust port 23 of the hopper 17 can be efficiently sucked and smoothly supplied into the underdrain 22 via the transport line 13.

[0055] In this case, since the functional material 16 transported riding on the Coanda spiral flow 31 moves without contacting the inner peripheral surface or the like of the transport line 13, the material 16 is not interrupted or does not clog, and thus the functional material 16 flowing into the underdrain 22 can be filled in a smooth and reliable manner.

[0056] As shown in FIG. 7, in the underdrain excavation apparatus 10, provided are the soil pressing members 20 protruding like a horizontal stabilizer on both side faces of the soil cutting shank 11. The soil pressing members 20 are disposed so that the respective members 20 have elevation angles of about 10 to 20 degrees toward the advancing direction, have fins 20 a hanging down from the side ends thereof, and forms a V-shape opening toward the front when seen in a plan view by the left and right parts thereof. Since the ground 21 torn off by the advance of the soil cutting shank 11 can be restored to the original state by the soil pressing members 20, collapse of the underdrain 22 bored by the underdrain borer 12 can be prevented, and the functional material 16 is not scattered.

[0057] In accordance with the present embodiment, the following advantages are obtained.

[0058] (1) In the underdrain excavation apparatus in which the bullet-like underdrain borer is pulled to excavate an underdrain in the ground and a functional material is filled in the underdrain, by connecting the gas flow generator which generates a gas flow by jetting a high-pressure gas supplied from the high-pressure gas generator into the tubular body with a functional material transport line, the functional material in the underdrain can be filled in a smooth and reliable manner while an underdrain is being excavated in the ground.

[0059] (2) By employing a Coanda spiral flow generator as the gas flow generator, the functional material can be conveyed extremely smoothly.

[0060] (3) By providing soil pressing members protruding like a horizontal stabilizer on both side faces of the soil cutting shank, since the ground torn by the advance of the soil cutting shank can be restored to the original state, collapse of the underdrain bored by the underdrain borer can be prevented, and the functional material is not scattered.

[0061] [Second Embodiment]

[0062] Next, an underdrain excavation apparatus 50 of the second embodiment is explained referring to FIG. 8. In the present embodiment, the same reference numerals as those in FIG. 1 to FIG. 7 are assigned to the members having the structures and functions similar to those of the underdrain excavation apparatus 10 described above, and the explanation thereof is omitted.

[0063] In the underdrain excavation apparatus 50 according to the present embodiment, a coupling member 53 is provided on the rear part of a bullet-like underdrain borer 51, and the distal end of a supply/drain pipe 56 drawn out from a supply/drain pipe supplying device 54 disposed adjacent to a starting point 52S of excavating an underdrain 52 is coupled with the coupling member 53 via a supplementary coupler 55.

[0064] Thus, the soil cutting shank 11 is advanced so that the supply/drain pipe 56, while being pulled into the underdrain 52 excavated by the underdrain borer 51, is laid, and the functional material 16 supplied via the gas flow generator 18 (not shown) and the transport line 13 can be filled in the space between the supply/drain pipe 56 and the underdrain 52. Since a Coanda spiral flow generator is employed as the spiral flow generator 18 also in this embodiment, the functional material 16 moves without contacting the inner peripheral surface or the like of the transport line 13 so that the material 16 is not interrupted or does not clog, and thus the functional material 16 is filled into the space between the underdrain 52 and the supply/drain pipe 56 in a smooth and reliable manner. The structures, functions, and the like of other parts are similar to those of the underdrain excavation apparatus 10 described above.

[0065] In accordance with this second embodiment, in the underdrain excavation apparatus in which the bullet-like underdrain borer is pulled so that a supply/drain pipe is laid in an underdrain while the underdrain is being excavated in the ground and a functional material is filled in the space between the underdrain and the supply/drain pipe, by connecting the gas flow generator which generates a gas flow by jetting a high-pressure gas supplied from the high-pressure gas generator into the tubular body with a functional material transport line, the supply/drain pipe is laid in the underdrain while the underdrain is being excavated in the ground, and the functional material can be filled in the space between the underdrain and the supply/drain pipe in a smooth and reliable manner.

[0066] [Third Embodiment]

[0067]FIG. 9 is a side view showing an underdrain excavation apparatus in use according to the third embodiment of the present invention; FIG. 10 is a rear elevation of the underdrain excavation apparatus shown in FIG. 9; FIG. 11 is a sectional view of the excavated underdrain; FIGS. 12A to 12E are enlarged views of a soil cutting shank part in the present embodiment, in which FIG. 12A is a side view, FIG. 12B is a front view, FIG. 12C is a plan view, FIG. 12D is a sectional view taken along the line B-B of FIG. 12A, and FIG. 12E is a sectional view taken along the line C-C of FIG. 12A; and FIGS. 13A to 13D are enlarged views of a clamp in the present embodiment, in which FIG. 13A is a side view, FIG. 13B is a plan view, FIG. 13C is a front view, and FIG. 13D is a sectional view taken on line A-A of FIG. 13A.

[0068] Underdrain excavation apparatuses 1OR and 101F according to the present embodiment are attached to the rear and the front of a bulldozer 102 having a caterpillar 103 on both sides thereof used as a traveling device. FIG. 9 shows a state where the apparatus is attached to the rear part. In the state of FIG. 9, the underdrain excavation apparatus 101 R comprises a soil cutting shank 111 held in a vertical position, a bullet-like underdrain borer 112 provided on a lower end of the soil cutting shank 111, a transport line 113 for feeding a functional material provided in the soil cutting shank 111 and the underdrain borer 112, a high-pressure air generator (not shown), a hopper 116 storing a functional material 1 15, and a gas flow generator 117 arranged between an exhaust port of the hopper 116 and the transport line 113 to be connected with each other, and a transport hose 118.

[0069] Stirring blades 119 feeding the functional material 115 toward the gas flow generator 117 connected to the exhaust port and a motor 120 which rotates/drives the stirring blades 1 19 are disposed on the bottom of the hopper 1 16. As shown in FIG. 12, horizontal-stabilizer-like soil pressing members 121 are provided on both side faces of the soil cutting shank 111.

[0070] The soil cutting shank 111 is supported by a clamp 124 which is opened/closed by cylinders 123 on a fixing device 122. Base end portions of the clamp 124 are rotatably supported on a fixing plate 122 a of the fixing device 122 by shafts 125, and middle portions thereof are supported by pins 126 which are attached to the distal ends of the rods of the cylinders 123. A hooking end portion 124 a of the clamp 124 supports the lower surface of a collar portion 111 a of the upper part of the soil cutting shank 111 so that the collar portion 111 a and the fixing plate 122 a are affixed to each other. In FIG. 12A, the clamp 124 of the left side indicated by a solid line shows a state where the collar portion 111 a is supported, and the clamp 124 of the right side indicated by a solid line shows a state where the cylinder 123 is shortened so that the collar portion 111 a is released. In the drawing, reference numeral 127 denotes a gasket provided for preventing air leakage of the transport line 113 of the functional material when the soil cutting shank 111 is supported.

[0071] The fixing device 122 and the body of the bulldozer 102 are coupled by a parallel link 128 and are driven to rise and fall by a lifting cylinder 129.

[0072] While the fixing device 122 having the above-described structure is provided also on the front part of the bulldozer 102, the hopper 116 is provided only on the rear part. The functional material 115 is supplied to the transport line of the front part of the fixing device 122 by the transport hose 118. The functional material is selectively supplied either to the front part or to the rear part of the fixing device 122 by operating a switching valve.

[0073] Next, an underdrain construction method using the apparatus according to the present embodiment is explained below.

[0074] Firstly, as shown in FIG. 9, the soil cutting shank 111 is supported on the fixing device 122 of the rear part of the bulldozer 102. By advancing the bulldozer 102 in the state where the underdrain borer 112 is arranged at a low position and the lower half of the soil cutting shank 111 is planted in the ground 130 so that the underdrain 131 is excavated in the ground 130, rice husks 115 supplied from the inside of the hopper 116 via the gas flow generator 117 and the transport line 113 are filled in the underdrain 131. FIG. 11 is a sectional view of a part of the underdrain 131 excavated.

[0075] The operation described above is executed before reaching a border ridge, and when the bulldozer 102 comes to a position where the bulldozer 102 cannot advance any more (or may be a position before that position), the clamp 124 of the fixing device 122 of the rear part is detached as shown in FIG. 14A. The bulldozer 102 is then backed straight while leaving the soil cutting shank 111 in the ground, and the bulldozer 102 is stopped at the place where the head of the soil cutting shank 111 comes to the position just below the lower part of the fixing device 122 of the front part. Then, the fixing device 122 is lowered as shown in FIG. 14B so as to clamp and fix the soil cutting shank 111. Thereafter, the bulldozer 102 is advanced so that the operation by the soil cutting shank 111 is resumed, and the underdrain 131 can be excavated up to a working groove 133 before a border ridge 132 as shown in FIG. 14C.

[0076] Next, another construction method by the bulldozer 102 with underdrain excavation apparatuses 101 R and 101 F of the present embodiment is explained below referring to FIGS. 15A to 15C. FIG. 15A is a side view showing the present construction method; FIG. 15B is an enlarged view of a main part; and FIG. 15C is an enlarged sectional view of an underdrain.

[0077] In this construction method, a coupling member 140 is provided on the rear part of the bullet-like underdrain borer 112, and the extremity of a supply/drain pipe 142 pulled out from a supply/drain pipe supplying device 141 disposed adjacent to a starting point 131S for excavation of an underdrain 131 is coupled with the coupling member 140 via a supplementary coupler 143.

[0078] Thus, the soil cutting shank 111 is advanced so that the supply/drain pipe 142, while being pulled into the underdrain 131 excavated by the underdrain borer 112, is laid, and the functional material 115 supplied via the gas flow generator 117 (not shown) and the transport line 113 can be filled in the space between the supply/drain pipe 142 and the underdrain 131.

[0079] Also in the present construction method, when the bulldozer 102 reaches a border ridge, the soil cutting shank 111 is detached from the fixing device 122 of the underdrain excavation apparatus IOR of the rear part, and the bulldozer 102 is backed so that the soil cutting shank 111 is fixed on the fixing device 122 of the underdrain apparatus 101F of the front part to advance the bulldozer 102, whereby the underdrain 131 can be excavated up to the working groove 133 of the border ridge.

[0080] In accordance with the third embodiment as above, the following advantages can be obtained:

[0081] (1) By installing fixing devices for a soil cutting shank on the front part and the rear part of a moving vehicle, after the soil cutting shank attached to the rear part is detached, the traveling device is backed straight, and the soil cutting shank is fixed by a soil cutting shank fixing device of the front part so that the traveling device is advanced, whereby an underdrain can be constructed up to a border ridge.

[0082] (2) Since the traveling device is only backed straight without doing a U-turn, an underdrain can be constructed within a short time and easily even in a narrow place.

[0083] (3) Since the traveling device is only backed straight, positioning of the soil cutting shank and the fixing device can be easily made, and work efficiency is improved.

[0084] (4) The operation of pulling the bullet-like underdrain borer so that the supply/drain pipe is laid in an underdrain while the underdrain is being excavated in the ground can be also executed a smooth and reliable manner.

[0085] In the embodiments above, although apparatuses in which a hydrophobic material such as rice husks is employed as a functional material are shown, by filling a water-holding material instead of the hydrophobic material as a functional material in an underdrain, water can be stored in an underdrain excavated in a desert or dry land. In such a system, water can be effectively supplied to the ground around the underdrain by appropriately supplying water from the outside a farmland by a supply/drain pipe,

[0086] While particular embodiments of the present invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only by the appended claims. 

What is claimed is:
 1. An underdrain excavation apparatus comprising: a soil cutting shank which is vertically held; a bullet-like underdrain borer which is provided on a lower end of the soil cutting shank; a pulling means; said soil cutting shank and said underdrain borer being pulled in a horizontal direction by the pulling means to excavate an underdrain in the ground; a functional material transport line provided in the soil cutting shank and in the underdrain borer, a functional material supplied via said functional material transport line being filled in the underdrain; and a gas flow generator generating a gas flow by jetting a high-pressure gas supplied from a high-pressure gas generator into a tubular body, said gas flow generator being connected with the functional material transport line.
 2. An underdrain excavation apparatus comprising: a soil cutting shank which is vertically held; a bullet-like underdrain borer which is provided on a lower end of the soil cutting shank; said soil cutting shank and said underdrain borer being pulled in a horizontal direction by the pulling means to excavate an underdrain in the ground while a supply/drain pipe is being laid in the underdrain, a functional material transport line provided in the soil cutting shank and in the underdrain borer, a functional material supplied via said functional material transport line being filled in the space between the underdrain and the supply/drain pipe; and a gas flow generator generating a gas flow by jetting a high-pressure gas supplied from a high-pressure gas generator into a tubular body, said gas flow generator being connected with the functional material transport line.
 3. The underdrain excavation apparatus according to claim 1, wherein said gas flow generator is a Coanda spiral flow generator which slantingly jets the high-pressure gas supplied from the high-pressure gas generator from an inner peripheral surface of the tubular body toward a central axis of the tubular body to generate a spiral gas flow along said inner peripheral surface.
 4. The underdrain excavation apparatus according to claim 2, wherein said gas flow generator is a Coanda spiral flow generator which slantingly jets the high-pressure gas supplied from the high-pressure gas generator from an inner peripheral surface of the tubular body toward a central axis of the tubular body to generate a spiral gas flow along said inner peripheral surface.
 5. The underdrain excavation apparatus according to claim 1, wherein said soil cutting shank having soil pressing members which protrude in a horizontal-stabilizer-like state on both side faces of the soil cutting shank.
 6. The underdrain excavation apparatus according to claim 2, wherein said soil cutting shank having soil pressing members which protrude in a horizontal-stabilizer-like state on both side faces of the soil cutting shank.
 7. The underdrain excavation apparatus according to claim 3, wherein said soil cutting shank having soil pressing members which protrude in a horizontal-stabilizer-like state on both side faces of the soil cutting shank.
 8. The underdrain excavation apparatus according to claim 4, wherein said soil cutting shank having soil pressing members which protrude in a horizontal-stabilizer-like state on both side faces of the soil cutting shank.
 9. The underdrain excavation apparatus according to claim 1, wherein the functional material is a hydrophobic material.
 10. The underdrain excavation apparatus according to claim 2, wherein the functional material is a hydrophobic material.
 11. The underdrain excavation apparatus according to claim 3, wherein the functional material is a hydrophobic material.
 12. The underdrain excavation apparatus according to claim 4, wherein the functional material is a hydrophobic material.
 13. The underdrain excavation apparatus according to claim 5, wherein the functional material is a hydrophobic material.
 14. The underdrain excavation apparatus according to claim 6, wherein the functional material is a hydrophobic material.
 15. The underdrain excavation apparatus according to claim 7, wherein the functional material is a hydrophobic material.
 16. The underdrain excavation apparatus according to claim 8, wherein the functional material is a hydrophobic material.
 17. The underdrain excavation apparatus according to claim 1, wherein the functional material is a water-holding material.
 18. The underdrain excavation apparatus according to claim 2, wherein the functional material is a water-holding material.
 19. The underdrain excavation apparatus according to claim 3, wherein the functional material is a water-holding material.
 20. The underdrain excavation apparatus according to claim 4, wherein the functional material is a water-holding material.
 21. The underdrain excavation apparatus according to claim 5, wherein the functional material is a water-holding material.
 22. The underdrain excavation apparatus according to claim 6, wherein the functional material is a water-holding material.
 23. The underdrain excavation apparatus according to claim 7, wherein the functional material is a water-holding material.
 24. The underdrain excavation apparatus according to claim 8, wherein the functional material is a water-holding material.
 25. An underdrain excavation apparatus comprising: a soil cutting shank which is attachably/detachably fixed on a fixing device which is provided on a traveling device; and a bullet-like underdrain borer provided on a lower end of the soil cutting shank; said soil cutting shank being pulled in a horizontal direction by the traveling device to excavate an underdrain in the ground; said fixing device being disposed on a front part and on a rear part of the traveling device.
 26. The underdrain excavation apparatus according to claim 25, wherein said underdrain borer is provided with a means for laying a supply/drain pipe in the underdrain simultaneously with excavating the underdrain by moving of the traveling device.
 27. The underdrain excavation apparatus according to claim 25, further comprising a means for filling a functional material supplied from the traveling device into the underdrain via a functional material transport line provided in the soil cutting shank and in the underdrain borer.
 28. The underdrain excavation apparatus according to claim 26, further comprising a means for filling a functional material supplied from the traveling device into the underdrain via a functional material transport line provided in the soil cutting shank and in the underdrain borer.
 29. The underdrain excavation apparatus according to claim 25, wherein the functional material is a hydrophobic material.
 30. The underdrain excavation apparatus according to claim 26, wherein the functional material is a hydrophobic material.
 31. The underdrain excavation apparatus according to claim 27, wherein the functional material is a hydrophobic material.
 32. The underdrain excavation apparatus according to claim 28, wherein the functional material is a hydrophobic material.
 33. The underdrain excavation apparatus according to claim 25, wherein the functional material is a water-holding material.
 34. The underdrain excavation apparatus according to claim 26, wherein the functional material is a water-holding material.
 35. The underdrain excavation apparatus according to claim 27, wherein the functional material is a water-holding material.
 36. The underdrain excavation apparatus according to claim 28, wherein the functional material is a water-holding material. 